Such angle measuring systems are used to measure rotary motions and rotational positions of a machine part, for instance, a shaft. The rotary motion is detected either incrementally or absolutely; the output measured value is a sequence of counting pulses, for example, a counter value or a code word. Corresponding angle measuring systems are used particularly in so-called pick-and-place machines in the manufacture of electronic components, or in machine tools for measuring rotary movements. The reproducibility or repeatability of the rotational angles of machine parts to a precision of only a few angular seconds is very important when working with pick-and-place machines, for instance. In particular, the absolute accuracy of the measuring results of an angle measuring system is crucial in the case of machine tools. Certain conventional angle measuring systems which have a separate bearing assembly of the component parts rotatable relative to each other.
The accuracy of an angle measurement is influenced by the quality of the angle scaling, its eccentricity and by the radial runouts of the bearing assembly or wobble errors.
U.S. Pat. No. 6,894,484 describes a bearing having an angle measuring device, in which a sensor unit is insertable as an exchangeable module in an entirely cylindrical recess of the outer ring.
This device has the disadvantage that the angle measuring systems manufactured according to this principle do not achieve the highest accuracies, are not sufficiently robust for many applications and, moreover, require a relatively great amount of space.